1. Field of the Invention
The present invention relates to a headlamp, and more particularly to a so called cornering headlamp which is formed so as to correct a light distribution characteristic which is caused by an inclination of a motorcycle or the like wherein a vehicle body is liable to be inclined with respect to a road surface.
2. Discussion of Relevant Art
FIG. 10 shows an example of such a conventional cornering headlamp 030 of the type mentioned as is disclosed in the Official Gazette of Japanese Patent Laid-Open No. 41484/1989, and an inclination sensor 021 which makes use of a gyroscope or ultrasonic waves is provided on a vehicle body 020 while a headlamp body 031 is constructed for pivotal movement around an optical axis relative to the vehicle body 020. When an inclination is detected by the inclination sensor 021, the headlamp body 031 is pivoted with respect to a road surface 022 in response to an output of the inclination sensor 021. The headlamp body 031 is pivoted by a driving device 023 which makes use of a motor or the like so that the degree of such pivotal movement may be such that the light distribution characteristic may be parallel to the road 22, that is, the light distribution characteristic may be the same as that when the vehicle body stands upright.
However, with a motorcycle, since the irradiation distance in an advancing direction upon cornering becomes shorter than that upon straightforward advancement, if the light distribution characteristic is only corrected to a horizontal direction, there is the possibility that the resulting effect cannot be exhibited sufficiently even though such complicated construction as described above is employed.
On the other hand, a headlamp is known which is constituted such that a predetermined light distribution pattern may be formed by stopping a part of the light radiating from a light source by means of a light stopping plate disposed on a front opening side of a reflecting mirror. A headlamp of the type mentioned is disclosed in the Official Gazette of Japanese Patent Laid-Open No. 158701/1988 wherein the light stopping plate is tilted leftwardly or rightwardly in response to an inclination of the vehicle body to change the light distribution pattern so as to normally present a good light distribution to required portions forwardly of the vehicle body.
The aforementioned Official Gazette No. 158701/1988 discloses a headlamp 01 as shown in FIG. 11. This headlamp is constituted such that a light source 03 is disposed at a first focus F.sub.1 of a reflecting mirror 02 having a reflecting face of an ellipsoid of revolution, and light reflected from the reflecting mirror 02 is focused upon a second focus F.sub.2 and then introduced into a convex lens 04, whereafter it is projected forwardly from the convex lens 04, and a stopping plate 05 is provided between the reflecting mirror 02 and the convex lens 04. The center of an upper edge of the stopping plate 05 is positioned on an optical axis X--X, while a left upper edge portion 05a extends horizontally at a same height as the optical axis, and a right upper edge portion 05b is inclined downwardly. Since light to be introduced into a lower half portion of the convex lens 04 from an upper half portion of the reflecting mirror 02 is stopped by the stopping plate 05, if light from the convex lens 04 is projected on a projection plane 06 positioned sufficiently forwardly, then a light distribution pattern wherein a lower portion is a bright portion 07 and an upper portion is a dark portion 08 is obtained. A right horizontal bright/dark boundary line 09a corresponds to a real image of the left upper edge 05a of the stopping plate 05, while a left, leftwardly upwardly inclined bright/dark boundary line 09b corresponds to a real image of the upper edge 05b. Since a focus F.sub.3 of the convex lens 04 is at a position a little forwardly of the stopping plate 05, however the degree of an out-of-focus condition of the image is low, and accordingly, the bright/dark boundary lines 09a and 09b obtained are clear lines.
While such a light distribution pattern is obtained when the vehicle body stands uprightly, if the headlamp 01 is inclined, for example, to the left-hand side together with the vehicle body, then the bright/dark boundary line 09b is tilted downwardly while the bright/dark boundary line 09a is tilted upwardly. Accordingly, in such instance, the stopping plate 05 is inclined to the right-hand side around the central point of the upper edge on the optical axis X--X to maintain the light distribution pattern shown in the figure.
To this end, the stopping plate 05 is supported for tilting motion as shown in FIG. 12. In particular, arcuate guided ribs 010, 010 centered at the central point O of the aforementioned upper edge are individually formed on the opposite faces of an intermediate portion of the stopping plate 05 in upward and downward directions while also a lower edge is formed in an arcuate shape centered at the aforementioned central point O and a gear 011 is formed on the lower edge. The stopping plate 05 is inserted into a slit 013 of an arcuate frame member 012 from above, and the guided ribs 010 are fitted for sliding movement in guide grooves formed in the opposite side walls of the slit 013 and having a same curvature as the guided ribs 010. The gear 011 projected downwardly from the frame member 012 is held in meshing engagement with a gear of a motor shaft (not shown), and when the motor is rotated, the guided ribs 010 are slidably moved along the guide grooves so that the stopping plate 05 is tilted leftwardly or rightwardly around the central point O, that is, the optical axis.
Since the headlamp disclosed in the aforementioned Official Gazette includes such stopping plate supporting and tilting device, the structure is complicated, and it cannot be avoided for the headlamp to be great in size.
By the way, a simplest method of supporting the stopping plate 05 for tilting motion around the central point O is to support the stopping plate 05 at the central point O by means of a bearing, but where such construction is employed, an upper half portion of the bearing will be projected upwardly above the central point O. However, since the bearing section is located very proximately to the position of a focus of the convex lens 04, a clear real image enlarged by the convex lens 04 is produced on the projection plane at a forward position, and the light distribution on a screen placed at a position spaced, for example, forwardly by 10 m is such as shown in FIG. 13a while the light distribution condition on a real road is such as shown in FIG. 13b. In those drawings, reference character 08a denotes a shadow (dark portion) produced by an image of the bearing section, and R denotes a road, R.sub.1 a road shoulder, and H a horizontal line. Needless to say, such light distribution is not preferable.